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The surface area of the particles – When the surface area of the reactant is increased more atoms are exposed and therefore available for collision. The surface area of the particles that we are using (calcium carbonate) can be increased by crushing it up.
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1www.wpbschoolhouse.btinternet.co.uk/page03/3_31rates.htm
Smaller pieces have a larger surface area so there are more collisions and therefore a faster reaction.
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Using a catalyst- A Catalyst is a substance that alters the rate of reaction but remains chemically unchanged at the end of it. It decreases the reactants activation energy, and speeds up the rate at which the reaction is taking place.
All of these variables are some how related to the collision theory. The collision theory is ‘the more collision between particles in a given time, the faster the reaction.’
For my experiment I have decided to vary the concentration of acid, there is a detailed description on the affect concentration has on the rate of reaction above (page 1); the table below shows the concentrations I used:
I have decided not to use a catalyst because I know that this would speed up the rate of reaction no matter what.
Prediction
I predict that the concentration of acid will affect the rate of reaction. I believe the rate of reaction will increase when there is a higher concentration of acid because the particles are more compressed and closer together, therefore giving them a greater chance of bumping and colliding into each other. I also think that as the concentration of reactant decreases the slower the rate of reaction will be. I think that the rate of reaction will be proportional to the concentration level. By doubling the concentration the rate of reaction will be twice as fast.
Plan
For my experiment I will be varying the concentration of acid, I decided to experiment this variable as I feel it will have a significant influence on the rate of reaction, hence enabling me to reach a valid conclusion.
In the experiment there will be a few things I will not be altering. These are surface area of the marble chips, volume of acid, mass of marble chips and the time. I will not change these as I feel that you need these for a fair experiment to be conducted.
Variables:
There are three types of variables; independent, dependant and controlled, I will be using all three types in my experiment.
- Independent- these are variables that you change.
- Dependant- these variables need to be measured.
- Controlled- these variables need to be kept the same throughout the entire experiment.
My variables:
- Independent- I will be changing the concentration of acid, because it will allow me in investigate whether the concentration of acid is proportional to the rate of reaction.
- Dependant- Time and volume of gas produced will need to be measured for me to progress and achieve accurate results in this experiment.
- Controlled- surface area of the marble chips, volume of acid, mass of marble chips and temperature of acid will need to be kept constant for my experiment to remain a fair test, also to enable me to receive precise results. I will also be using the same equipment throughout my experiment to ensure fair testing.
I think that after conducting this experiment I will find out that the collision theory is correct and I will also find that with my experiment, as the variable changes so will the rate of reaction.
I conducted a trial experiment to make sure that there was nothing wrong and that there were no glitches in the way in which our experiment was going to be conducted.
Preliminary test
Apparatus:
- A bowl of water- Needed to place measuring cylinder in
- A measuring cylinder- Needed to measure amount of carbon dioxide released
- A conical flask- Will lead the gas to the measuring cylinder
- A delivery tube- One end will be attached with a bung
- A stop watch- Will be used to measure the time
- Some marble chips- Needed for reaction to take place
- 1M hydrochloric acid- Needed for reaction to take place
- Retort stands and clamp- to hold the measuring tube in place
- Safety goggles
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25 cm3 plastic syringe
- Top-pan balance
- Bung
Method
- Firstly I measured the mass of 7 marble chips; they all needed to have the same mass to ensure a fair test. In the trial test we chose to use 30g marble chips but found they were not very responsive, therefore we increased the mass to 90g and this provided us with consistent results.
- The next step was to dilute the acid concentrations with water to vary the acid concentration levels.
- After all the reactants were ready, the equipment had to be set up. The diagram above shows the way in which my apparatus was set up.
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After everything was ready and set, we began experimenting. Firstly we started with solution 1, which consisted of 25cm3 hydrochloric acid and no water. Each individual solution was experimented for 90 seconds. The reason for this is explained below.
- We then trailed the rest of the solutions, the description of each solution can be found on page 3.
I chose to use the “measuring the displacement of water in a measuring cylinder” method because I consider this method to be the most accurate, since the cylinder will allow volumes to be measured correctly.
Safety
Whilst carrying out the experiment it is essential to work in a safe environment. It was vital to wear goggles during the whole experiment. Also, I must be careful especially with the stronger molarity acid because it will be corrosive so I must make sure I do not spill it on my hands or more especially in my eyes. One way to avoid this is to be extremely careful and wear safety goggles. In this experiment I will have to make sure I am careful with all glassware in case it breaks and if it does to make sure it is immediately cleaned up.
What I discovered from my preliminary work?
- Highest concentration- the highest concentration I am going to start off with is 1m, because whilst testing 2m, I discovered that the reaction was over too quickly and this could lead to me not seeing consistent patterns.
- Lowest concentration- the lowest concentration I will use in my final experiment is 0.4 molar acids, for the reason that the 0.2 molar was not responsive in my trial test as you can see in the results table below.
- I decided to measure the volume of gas every 10 seconds, because I felt this was the most appropriate as there was a change approximately every 10 seconds.
- I chose to test the experiment for 90 seconds, as I felt this would enable me to receive reliable repeats and possibly a clear pattern.
Preliminary test results
As you can see the 2m and 0.2m do not fit in accordingly with the others. For this reason I have chose not to include them in my final experiment.
Results of final experiment
I repeated the method process twice, I would have preferred to repeat it three times but did not have much time left. (Method can be found on page 5), to ensure accuracy of results and to solve any anomalous results.
The columns in red represent the averages.
Analysis
From my results it can be seen that when the concentration of the acid is higher the rate of reaction is once again faster. This is because there are more particles and they are forced together, as a result of this they react faster. Once again my results clearly demonstrate that an increase in concentration makes the rate of reaction faster. In my prediction I stated that the rate of reaction would be proportional to the concentration. My graphs to a certain degree agree with this. When I worked out the rate of reaction from the gradients of the lines that I drew, I noticed that the rate of reaction was almost twice more fast for the 1M solution of acid than the 0.5M solution. This shows that the rate of reaction is proportional to the concentration. All my graphs showed strong positive correlation, in addition my graphs show the higher the concentration the steeper the line. The steeper the line the faster the rate of reaction. It is therefore evident from my results and graphs that concentration increases the rate of reaction. My results obey the collision theory.
Evaluation
Generally my results were reliable in that they showed that an increase in temperature increases the rate of reaction. However I feel that more tests may have given a better conclusion regarding the rate of reaction being proportional to the concentration. The results that I obtained were sufficient enough to reach a conclusion. My graphs all share a positive correlation showing that an increase in concentration affects the rate of reaction. My results were in agreement with the collision theory. I feel that by conducting the experiment twice for a change in concentration was not enough. Because I believe that from to results an accurate average can not be received. If the tests had been carried out more than three times for each solution the results would have given a more accurate mean value. With more tests there is a smaller margin for error. ‘Freak results’ would be masked by other results.
I feel I was successful in maintaining the experiment a fair test, although I found controlling the mass of the marble chips difficult. If I were doing this again, I would get digital scales to help me achieve accurate measurements. However I believe I was successful whilst diluting the acid, using a cylinder and syringe helped.
To extend the investigation I could use powdered marble chips to see if this created a difference, or try adding a catalyst which would speed up the experiment, but would not be lost at the end, to compare with the results I have now, to see how the difference of speed of the reaction changes. I could also test other factors such as surface area and temperature to move the experiment further.